A study on the presence of hydrogen spillover on carbon-supported platinum catalysts was conducted. CO and H2 uptakes were determined at ambient temperature on Pt/C catalyst variously diluted with carbon. The effect of H-2 spillover on benzene hydrogenation over Pt/C and diluted Pt/C was studied. From chemisorption results a direct observation of hydrogen spillover at room temperature was made. Activity data suggest that benzene hydrogenation occurs both on Pt/C and carbon diluent due to hydrogen spillover. The specific activity increased to a dilution level beyond which it became constant. This fact was further confirmed by H-2 uptake measurements. Arrhenius plots of various diluted samples show an equal slope resulting in a uniform value for activation energy. The mechanism of benzene hydrogenation due to spilled over hydrogen on Pt/C appears to be same as on Pt/gamma-Al2O3.